The overall aim of the proposed project is to test our hypothesis that the characteristic disturbance of hemoglobin synthesis in sideroblastic anemia and erythroleukemia is due to an abnormality in the cellular uptake and transport of iron in erythroid precursor cells. This hypothesis is being tested by studying metabolic, biosynthetic and membrane transport functions of the erythroid cells in these diseases. Increased iron uptake was shown in sideroblastic erythroid cells and may be due to a loss of preferred uptake from one metal-binding site of transferrin. Studies on the identification of the transferrin receptor of erythroid precursor cells are being carried out using two different methods. Incubation of erythroid cells with fluorescent-labeled transferrin and binding assays of transferrin, immobilized on agar gel bead columns, with membrane polypeptide of erythroid cells are used. Selective modifications of intact cells and isolated transferrin-binding membrane polypeptides are produced by treatment with specific enzymes of mild chemical means. The effect of lipid peroxide formation, found to be markedly increased in erythroid precursors of iron-loading anemias, on rate of glycolysis and hexose monophosphate shunt activity will be evaluated. Effect of iron chelators, sulfhydryl reagents and antioxidants on these metabolic activities will be determined. Ferritin and globin synthesis in erythroid cells are compared and studied with respect to possible competition for substrate and effect of size of pre-existing intracellular iron stores.